This application relates generally to filtration systems and, more particularly, to a water recirculating system for use in producing fish.
Raising fish in water recirculating systems requires nitrification treatment systems that maintain acceptable levels of ammonia and nitrite within a water supply. A water recirculating system needs to be able to oxidize an ammonia load that is generated by fish as a result of daily fish feedings.
FIG. 1 illustrates one type of prior art filtration system 10 that may be used in a water recirculating system. The filtration system 10 includes a chamber 12 that contains microbeads 14. Microbeads 14 are sufficiently buoyant such that they float on top of filtered water 16 that collects in the bottom of chamber 12. The microbeads 14 on the bottom are partially submerged in filtered water 16 because they support the weight of the microbeads 14 located above them.
Contaminated water 18 is delivered to filtration system 10 from a number of potential sources, including fish raising tanks where the water supply is contaminated with unsatisfactorily high ammonia loads. Contaminated water 18 is supplied to chamber 12 from above microbeads 14 using any method that uniformly distributes contaminated water 18 over microbeads 14, such as nozzles 13 arranged in a uniform pattern. Gravity forces contaminated water 18 downward through microbeads 14 where it collects in the bottom of chamber 12. Contaminated water 18 applies a force to microbeads 14 as it impacts microbeads 14 such that contaminated water 18 submerges some additional microbeads 14. An exit pipe 20 circulates filtered water 16 back to the contaminated water source.
Microbeads 14 provide a substrate for bacterial growth during operation of filtration system 10. The bacteria on microbeads 14 utilize the ammonia and nitrite as nutrients for even further bacterial growth. The bacterial growth on microbeads 14 also tends to reduce the buoyancy of microbeads 14. Heterotropic bacteria living on the same beads utilize fine organic solids as nutrients for growth resulting in water polishing and general improvement in water quality.
One disadvantage of using a system 10 that includes microbeads 14 is that such systems are limited in size. In systems with large chambers, the strong buoyancy of microbeads 14 causes microbeads 14 to short circuit the flow of water through microbeads 14 in some areas of the chamber. Short circuiting the flow of water through microbeads 14 inhibits the ability of the bacteria on microbeads 14 to oxidize ammonia loads in the water passing through microbeads 14.
The size limitations associated with conventional filtration systems that include microbeads makes it necessary to utilize several chambers when oxidizing commercial ammonia loads (e.g., 9 kilograms TAN per day) that are generated from commercial fish feedings (e.g., 300 kilograms per day). The large number of chambers that are required to handle commercial ammonia loads adds unwanted expense to systems that include microbeads 14.
A filtration system having a chamber with a hydraulic loading area that is divided into a plurality of cells such that each cell has a hydraulic loading area less than 2.3 square meters. The system further includes a filter media, such as microbeads, positioned in each cell to filter water passing through the chamber. In some embodiments, the microbeads are spherical and have diameters between 1 mm and 3 mm.
The size limitation of conventional microbead filter systems is addressed by dividing the hydraulic loading area in a large chamber into cells with smaller hydraulic loading areas. The smaller hydraulic loading area through each cell promotes efficient filtering by bacteria that grows on the microbeads in each cell.
Another aspect relates to a water recirculating system for use in producing fish. The water recirculating system includes a fish raising tank that provides an environment for fish to grow. A supply system, such as a pumping system, delivers water from the tank to a filtration system. The filtration system includes a chamber with a hydraulic loading area that is divided into a plurality of cells with smaller hydraulic loading areas. Filter media, such as microbeads, are positioned in each cell to filter the water received from the supply system. A delivery system returns the filtered water back to the tank.